High-resolution radar imaging is a requirement in a variety of remote sensing applications. For example, radar reflectivity imaging is used in various security, medical, and through-the-wall imaging (TWI) applications. Whereas the down-range resolution is mostly controlled by the bandwidth of the transmitted pulse, the cross-range (azimuth) resolution depends on the aperture of the radar sensors. Typically, the larger the aperture, the higher the image resolution is, regardless of whether the aperture is physical (a large antenna) or synthetic (a moving antenna). Currently, the increase of the physical size of antenna leads to a significant increase of the cost of the radar system. To that end, a number of radar imaging systems use synthetic-aperture methods to reduce the size of the antennas and the cost of radar imaging. For example, synthetic-aperture radar (SAR) and inverse SAR (ISAR) use the relative motion of the radar antenna and an object in the scene to provide finer spatial resolution with comparatively small physical antennas, i.e., smaller than the antennas of beam-scanning radars.
However, the small size of physical antennas of radar systems makes the tracking of deformable moving objects difficult. Specifically, tracking objects exhibiting arbitrary motion and deformation requires tracking sensitivity with minimum resolution greater than the resolution of the physical antennas resulting in an impractical cost of the radar imaging system. To that end, conventional radar and/or other electromagnetic or acoustic wave imaging systems require the object to be standing still in the scene or moving in a very controlled rigid motion. Even for the rigid motion, conventional radar imaging systems require a challenging tracking step to estimate the motion parameters of the moving object using only the radar data, before a radar image can be formed, see, e.g., Martorella 2014. (Martorella, M. (2014). Introduction to inverse synthetic aperture radar. In Academic Press Library in Signal Processing (Vol. 2, pp. 987-1042). Elsevier.)
Therefore, there is a need for radar imaging systems and methods suitable for tracking an arbitrarily deformable moving object, using radar antennas of comparatively small aperture.